The present invention relates to a method of producing a container body having a butt welded longitudinal seam from a sheet metal blank, the blank being preformed in such a manner that its side edges are spaced uniformly from one another over its entire length, and are each at the same distance from the axis of the finished container. The invention also relates to an apparatus for performing the method, the aparatus being of the type which includes an outer guide arrangement; an upper guide rail having two lateral guide grooves, both at the same height, which--when seen in the direction of advance--at the beginning lie slightly above the final shape of the finished container and, at the end, lie at the level of the final shape of the container, the grooves having bottoms which--in the horizontal plane--are spaced from one another such that the value existing at the start of the guide rail steadily decreases toward its end; and a heat source disposed downstream of the guide rail, when seen in the direction of advance.
U.S. Pat. No. 4,354,090 discloses an apparatus for producing container bodies having a butt welded longitudinal seam, in which the side edges of the sheet metal blanks are held by external rollers and are guided during their advance in lateral longitudinal grooves of a so called Z-bar. Two guide grooves--when seen in the direction of advance of the blanks--adapt themselves from different heights to a common height. The groove bottoms of the guide grooves extend over the entire length of the Z-bar, each time to a common center plane. Since the respective pieces of the container body reach their final shape upon leaving the Z-bar, the side edges, caused by the external rollers, lie flush against one another and are then subjected to the influence of heat from a laser source. Since the side edges already lie against one another over a certain length when the thermal energy is applied, there occurs merely a fusion or sublimation welding process in which the material is heated to the melting phase or to the vapor phase, and flows off in part as metal vapor within the "vapor channel" formed in the joining groove. The vapor condenses at the already hardened weld seam and finally hardens to form a weld seam. At higher welding rates or more than about 0.5 m/s, this may produce turbulences in the melt and thus irregularities in the weld seam.
U.S. Pat. No. 4,635,841 discloses another device for producing container bodies having a butt welded longitudinal seams. The guide rail of this device is provided with two guide grooves of identical height for the side edges of the sheet metal blanks. Seen from the side, these guide grooves follow a path which is increasingly curved downwardly. The groove bottoms are spaced from one another by an amount which decreases steadily from a finite value at the beginning of the guide rail to almost zero at the end of the guide rail. According to the teaching of U.S. Pat. No. 4,635,841, the side edges of the blanks are to lie against one another, due to the geometric relationships after leaving the guide rail following the initial contact, along the entire section after leaving the guide rail between the end of the rail and the welding location. Here again, the section of the blank leaving the guide rail obviously has already attained its final geometric shape before the actual joining process, and there occurs a fusion or sublimation welding process with the already mentioned drawbacks.